I'm glad to see that a few woke up and included a few classics in their dream collection! who wouldn't want a 300SL Gullwing, a 250 GT California SWB, a Miura, a Bugatti 57C Atalante, a Ford GT40, and the list goes on... I think you need a mix of old and new, hardcore and GT/luxury, so that all six can give you the full range of the spectrum, and that way you can have a totally different driving experience EACH day of the week :-)

I'd go for (in no particular order):

1. Ferrari 250 GT California SWB
2. Rolls Royce Phantom Drophead (2008)
3. '66 Mustang Shelby 390 GT (only 3 built with a big block in that year) - gotta include a muscle car :-)
4. Bugatti 57C Atalante
5. Porsche 993 GT2 (the most powerfull air-cooled, turbo-charged, 2 wheel-drive 911, I think)
6. Lambo Reventon (just gotta have a cutting edge supercar)

I was so tempted on making a strictly Ferrari list, or a strictly retro list, but I thought I take time and be creative